Fuel tank



Oct. 28, 1947. w. R. HoovER 2,429,688

FUEL TANK Filed April 1'7, 1943 2 Sheets-Sheet 1 ATTORNEY W. R. HOOVERFUEL TANK Filed April 17, 1943 Oct. 28, 1947.

2 Sheets-Sheet 2 f Av Lau .g l TTORNE Patented Oct. 28, 1947 UNITED FUELTANK Walter R. Hoover, Mishawaka, Ind., assigner to United States RubberCompany, New York, N. Y., a corporation of New Jersey Application April17, 1943, Serial No. 483,457

4 Claims. (Cl. 154-435) This invention relates'to bullet-sealing fueland I oil tanks for combat vehicles, particularly airplanes.

- It is usual to provide combat; Vehicles with bullet-sealing tanks soconstructed that they inherently and automatically tend to close andseal holes made by projectiles. The bullet-sealing characteristics maybe due to inherent chemical or physical characteristics of the materialused, and may be obtained by various constructions of Walls embodyingvarying kinds of rubber compositions and other elastic materials, as isknown in the art. Usually such bullet-sealing walls are flexible, andare'contained in and supported by outer containers made of metal andformed by the Walls and bulkheads of the vehicle itself.

It has been found that when such a bulletsealing tank is enclosed in ametal outer container, such as the aluminum skin of an airplane wing, aprojectile entering the tank drags the metal with it, forming sharp andirregular edges on the metal skin, which remain attached to the skin andproject in to the hole formed by the projectile in the sealant layer.This prevents the sealant material from closing on itself to seal thehole. This action of the metal is referred to as flowering. The exithole formed in the metal outer container by the projectile as it leavesthe tank is frequently larger than the entering hole. In addition theextremely high hydraulic pressure developed by the impact of theprojectile in the liquid in the tank tends to deform the metal outercontainer into a sphere, and this leaves the exit wall bumped or dishedaway from the flexible sealant wall that it formerly supported. Theresult is that either due to this deformation or to the tearing away ofthe metal of the wall by a leaving projectile, or both, a large area ofthe ilexible sealant wall about the hole is left unsupported against thestatic pressure of the liquid inside. This pressure bends the sealantlayer outward, and tends to prevent the edges of the hole from comingtogether so that they may be sealed to close the hole.

In attempting to eliminate the disadvantages described, it has beenproposed to enclose the sealing tank within a relatively stiff,non-flowering container or liner (made for example of plywood) betweenthe sealant layer and the outer metal container. All such proposalswhich have come to my attention have various disadvantages, and none ofthem meet -all of the conditions imposed on planes in actual combat.

I have discovered that certain novel combinations of materials whenformed into a sup- 2 porting Wall for a bullet sealing tank preventl thecarrying of metal into the sealing tank from outer containers, andpermit a projectile to pass I through the supporting wall leaving anopening no larger than the projectile, and in some 'inistances smallerthan the projectile, and that these characteristics are preserved overwide ranges of temperature. I have also discovered that such novelcombinations of materials are substantially completely resistant tooils, aro-2 matic hydrocarbon fuels, and to water, and to mixtures ofthem and that all these characteristics are maintained over wide rangesof temF perature. The fact that the projectile in passing through suchmaterial makes a clean-cut hole no larger than the projectile is duelargely to the high tear resistance, toughness and elastic propertieswhich render the material substantially rigid or stiff with respect toforces of low intensity making it suitable for supports for heavy tanksof fuel, and highly flexible and e1as tic, tough and non-shattering whenexposed to the forces incident to impact by high velocity projectileshaving great kinetic energy.

It is, therefore, an object of the invention to provide a materialparticularly adapted to supports for self-sealing fuel tanks which ischemically inert to water, oil and aromatic hydrocarbon fuels, which istough and nomshattering, which exhibits rigidity to low velocity impactsand exhibits elasticity and fiexibility to high velocity impacts, andwhich will retain these characteristics throughout wide ranges oftemperature.

Other objects and advantages of the invention will be apparent from theaccompanying description and annexed drawings in which:

Fig. 1 is a section taken through a portion of an airplane Wing and tankembodying the invention;

Fig. 2 is an enlarged sectional view of a portion of a tank support,corresponding to Fig. l;

Fig. 3 is a section of a portion of a wall of a fuel tank not embodyingthe invention, showing the action of an entering projectile;

Fig.` 4 is a sectional view corresponding to Fig, 3 of a tank showingthe action of a leaving projectlle;

Fig. 5 is an elevation of the tank taken from the right of Fig. 4;

Fig. 6 is a sectional view of a portion of a wall of a bullet sealingtank embodying the invention showing the action of an enteringprojectile;

."liig. 7 is a corresponding section of a tank embodying the inventionshowing an intermediate stage of ra projectile leaving the tank;

Fig. 8 is a view corresponding to Fig. 7 just after the projectile hasleft the tank;

Fig. 9 is an elevation taken from the right of Fig. 8 at a planerepresented by the line S-F-S; and

Fig. 10 is a section on the line iii-i0 of Fig. 8.

Figs. 3 to 5 representl the effect of projectiles on fuel tanks of priorconstruction which my invention seeks to eliminate. In these figuresdesignates the flexible bullet sealing wall of a fuel tank which iscontained in an aluminum alloy outer container or housing 22, A bullet24, represented as having just passed through the wall, has formed ahole into which the metal wall 22 has flowered, forming an obstruction26 in Fig. 3 which holds the hole open. This action is typical ofprojectiles entering self-sealing tanks enclosed in metal housings.vObviously such a hole will continue to leak, causing loss of fuel, ifnot destruction of the vehicle from fire.

Figs. 4 and 5 show a typical action of a projectile leaving the tank.After a projectile of the form shown in Fig. 3 enters a tank it usuallydoes not maintain its alignment with its own trajectory, but tumbles endover end, and consequently is frequently traveling sidewise when itpasses through the exit wall as shown in Fig. 5. The metal wall 28 isboth deformed or dished outwardly by the pressure of the liquid in thetank under the impact of the projectile, and a large jagged exit hole 30has been made by the bullet. This deformation has carried the wall 28away from the flexible wall 32 on the exit side ofthe tank, leaving thewall 32 unsupported against the pressure of liquid within the tank.I

Under the influence of this pressure the Wall 32 is pressed outward andthe hole 34 made by the bullet is held open, as shown in section in Fig.4 and as indicated in elevation by the dotted lines in Fig. 5. This holewill also continue to leak because its edges are held apart and closingand sealing are prevented.

The above described disadvantages are eliminated by my invention,constructed as shown in Figs. 1 and 2 and in Figs. 6 to 10. Apuncturesealing tank having walls 40 of any suitable construtcion iscontained in a metal compartment, housing or outer container formed bythe metal a novel combination of materials and have novelcharacteristics which appear to be peculiar to this combination ofmaterials, Referring to Fig. 2, each panel is preferably constructed oflayers 48 of glass cloth impregnated and bonded together by a suitableresin. For clarity the resin is indicated by the enlarged or exaggeratedlayers 50. In practice the layer of resin on the outside of the glasscloth is extremely thin or even imperceptible.

The glass cloth is any suitable cloth or fabric woven from yarn spunfrom ne glass fibers, as known in the art, but the thickness and nurnberof threads are such that the glass cloth alone has a tensile strength inexcess of about 45,000 pounds per square inch.

Both the chemical and physical characteristics of the bonding resin areimportant in order that the resulting panel may have the necessarychemical and physical qualities. The panel must be inert to lubricatingoils, to aromatic hydrocarbons, to water, and to mixtures of these. Ithas been found for example, that some materials which appear inert toaromatic hydrocarbons plates or sheets 42, which are usually integralparts of a vehicle, such as the airplane wing 44. One good practicalconstruction, known heretofore, for making the walls 40 puncture sealingis to form these walls of natural or synthetic rubber that isunvulcanized, and cover the inner face of these walls with a protectingi'llrn of synthetic rubber that is capable of resisting the action ofthe tank contents; the outer face of the unvulcanized materialypreferably has a strong backing fabric of the cord type securedthereto. Between each of the walls 40 and the corresponding metal plate42, I, in accordance with the present invention, insert a hardboardpanel or sheet 46, constructed as shown in the enlarged section, Fig. 2.Usually the flexible inner tank formed by walls 40 is slightly largerthan the compartment formed by the plates 42 into which it is inserted,in order to insure the firm and continuous support of the walls 40 bythe Walls 42, as is known in the art. 'I'he panels 46 are cut to t thecorresponding walls 40 and are placed between the tank and the plates42. When the fuel containing tank 40 is larger than tlie compartment ofthe plane in which it is inserted it and to water when tested with anyof these substances alone, for some reason are not wholly vinert towater and aromatic hydrocarbons when shaken together in the samecontainer. This is a condition frequently met with in airplanes due tocondensation of moisture from the air in fuel tanks,

As to physical characteristics, the panel must be suiciently stiff orrigid to function as a support for flexible walls under the head ofliquid ordinarily encountered in airplane fuel tanks, yet it must besufficiently elastic to receive without permanent deformation the suddenincrease of pressure of liquid when the tank is struck by a projectile.struck, and so will break cleanly, leaving asmall hole. And finally allthese characteristics must be maintained throughout wide temperatureranges.

I have found that glass cloth impregnated and bonded together with athermo-setting resin made by the Columbia Chemical Company, Barberton,Ohio, and sold under the designation 0R39 is effective in accomplishingthe objects of my invention. I do not know the composition of thisresin, but it is believed to be a polymer of the diallyl ester ofoxydiethylenedicarbonic acid. Further information about this resin isgiven on page 143 of "Plastics Catalog, the 1944 Encyclopedia ofPlastics, published by Plastic Catalogue Corporation, 122 East 42dStreet, New York, N, Y. The resin itself, when polymerized has a tensilestrength of about 3000 pounds per square inch. In practice two or moresheets of glass cloth, suicient to give the desired thickness and havinga tensile strength of 45,000 pounds per square inch are superposed andsaturated with the CR39 resin, held flat with or without pressure, andbaked at a temperature of about 160 F. for about four hours andsubsequently It must not shatter nor tear when method of making same.For example, two layers ofheavy glass cloth impregnated and bonded inthis manner provide a panel .050" thick having a density of .40 poundper square foot and a tensile strength of about 29,000 pounds per squareinch. The panel contains about 50% resin and 50% glass cloth, andappears quite rigid, and will adequately support a large `area offlexible bullet-sealing wall against the static pressure of liquidattained in the usual fuel tank. The panel does not shatter or tear whenstruck by a .50

caliber lbullet at temperatures above about -30 F., and it does notsoften or lose its stiffnessor Y elasticity at temperatures below about160,F. The material is inert to oil, aromatic hydrocarbonfuels and waterbetween these temperatures.

I have also made satisfactory panelsy by bonding and laminating glasscloth with a resin sold by the American'Cyanamid Company under thedesignation Laminac- P4122, the composition of which I do not know, butwhich I believe to be a mixture of an alkyd resin anda polymerizableol'ene (styrene) which is further described on page 137 of the abovementioned publication. When using this resin, I proceed as describedabove with respect to the CR39 resin, but bake the laminate about twohours at a temperature of about 220 F. I have also made successfulpanels with a resin marketed under the name .Plaskom a melamine resinmade by the, Plaskon Division of Libbey-Owens-Ford Glass Company ofToledo, Ohio, the composition of which I do not known, but which Ibelieve to be a urea formaldehyde type resin; with a resin marketedunder the name Melmac made by the American Cyanamid Co., PlasticDivision, New York, N. Y., the composition of which I do not know, butwhich I believe to be a melamine resin.

The action of panels made as described above is illustrated in Figs. 6to 10. The bullet-sealing container 09 is enclosed by the outer metalcontainer 42 and panels d6 made in accordance with my invention. In Fig.6 the bullet 2d has just pierced the walls in entering the tank, leavinga clean hole in the metal wall 42 and the panel 46,

which permits the edges or faces of the hole in the wall 40 to cometogether along the line or seam 52. They are urged together by theinherent action of the wall 40, and sealed by the the inherentcharacteristic of the panel to form a clean break or hole, when backedup by the wall 40 and the head of liquid within the tank, and whenstruck by a projectile of high velocity. Likewise the inherent'stiffnessof the panel is such that the metal is mechanically held againstflowering into the wall 40, and a clean hole is formed 'in the metal, of`approximately the size of the projectile. Thus, if the projectile issmall, for example of a diameter of 20 millimeters, the unsupported areaof the wall 40 is not sumcient to prevent it sealing itself.

- Referring to Figs. 9 and 10 it has been observed that a projectile,tumbled and leaving the tank sidewise, leaves a hole in the panel whichis smaller than the proiile of the projectile, as shown at 54. There area number of cracks, as answered at 56. leading from the hole 54, and

pass through, then snaps back as shown in Figs.

7 and 8. Fig. 8 shows a section of an actual exit wall, after theprojectile has passed through. The wall 42, being unsupported againstthe impact of the bullet. flowers away from the bullet, leavingalargehole as indicated at 5B. There may also be some dishing or permanentdeformation of the wall d2, but my experience has been that this islargely reduced or completely eliminated where the-panel 46 is used.Itis believed that the action of the composite wall at the in stant theprojectile passes through it is as illustrated in Fig. 7. The portion ofthe panel B6 enclosed within the line 54 in Figs. 9 and 10 is carriedaway. the panel is cracked as indicated at 56 and the parts between thecracks 56 bend outward as indicated in Fig. 7 yto permit the bullet topass. When the bullet has left the wall, the portions of the panel d5between the cracks snap back into the position shown in Fig. 8, pressingthe sealant layer d0 back into its former plane and permitting the edgesor faces of the hole to close upon themselves and be sealed. 'The resultis a large hole 58 in the metal wall 42, a hole in the panel d6 smallerthan the bullet and surrounded by cracks, and a tightly closed seam 00in the sealant wall.

Experiments indicate that the above action occurs throughout the wideranges oi temperature indicated above, and under substantially allconditions of shooting which are encountered in combat.

Havingthus described my inventiomwhat I claim and desire to protect byLetters Patent is:

1. A reservoir for liquid hydrocarbons comprising in combination anvinner container including a flexible wall of puncture-sealing material,an outer container surrounding the inner container and including a metalwall that indirectly supports the ilexible'wall, and a stiff, elastic,strong, tough and shatter resistant panel between. and in contact withsaid walls and which is adapted to be installed before the innercontainer, said panel comprising a woven glass cloth impregnated with aresin and characterized by the property that an entering projectilepassing through the panel and walls will cut a clean hole -in the panelno larger than the projectile and thereby prevent the metal of theadjacent wall from being flowered into the wound of the sealingmaterial, and the panel will not split under the high hydraulic pressureof the liquid displaced by the projectile traveling through the liquidbut will spring back after it is pierced by the leaving projectile tohold the sealing material from bulging.

2. A reservoir for liquid hydrocarbons comprising in combination aninner container including a ilexible wall of puncture-sealing material,an outer container surrounding the inner container and including'a metalwall that indirectly supports the iiexible wall, and a stiff, elastic,strong, tough and shatter resistant panel between and in contact withsaid walls and which is adapted to be installed before the innercontainer, said panel comprising a plurality of layers of woven glasscloth impregnated and bonded together with a. resin having a tensilestrength of about 3000 pounds per square inch and characterized by theproperty that an entering projectile passing through the panel and wallsWill cut a clean hole in the panel no larger than the projectile andthereby prevent the metal of the adjacent wall I' ing in combination aninner Acontainer including a flexible Wall of puncture-sealing material,an outer container surrounding the inner container and including a metalwall that indirectly supports the exible wall, and a stii, elastic,strong, tough and shatter resistant panel between and in contact withsaid walls, said panel comprising a plurality of layers of woven glasscloth impregnated and bonded together with a resin an'clhaving a tensilestrength of about 29,000 pounds per square inch and characterized by theproperty that an entering projectile passing through the panel and wallswill cut a clean hole in the panel no larger than the projectile andthereby prevent nated and bonded together with a resin, the resin havinga tensile strength-of about 3000 pounds the metal of the adjacent wallfrom being flowered into the wound of the sealing material, and thepanel will not split under the high hydraulic pressure of the liquiddisplaced by the projectile travelling through the liquid but willspring back after it is pierced by the leaving projectile to hold thesealing material from bulging.

4. A reservoir for liquid hydrocarbons comprising in combination aninnner container including a flexible wall of puncture-sealing material,an outer container surrounding the innercontainer and including a metalwall that indirectly supports the flexible wall, and a stiff, elastic,strong, tough and shatter resistant panel between and in contact withsaid Walls, said panel comprising a pluralityof layers of Woven glasscloth impreg per square inch and the panel having a tensile strength ofabout 29,000 pounds per square inch and charanterized by the propertythat an entering projectile passing through the panel and walls will cuta. clean hole in the panel no larger than the projectile and therebyprevent the metal of the adjacent wall from being flowered into the`Wounds oi the sealing material, and the panel will not split under thehigh hydraulicvpressure of the liquid displaced by the projectiletraveling through the liquid but will spring back after it is piercedbythe leaving projectile to hold the sealing material from bulging.

WALTER R. HOOVER.

REFERENCES, errno The following references are of record in the file ofthisv patent:

UNITED STATES PATENTS

